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AERCO International, Inc.
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100 Oritani Dr.
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Blauvelt, NY 10913
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Ph: 800-526-0288
GF-115-H
OMM-0083_0B
Modulex MLX Series Gas Fired Boiler System
Operation and Maintenance Manual
Chap 13: Boiler
Water Quality
13.1 Modulex Boiler Water Chemistry
13.1.1 Reaction of Metals to Water Chemistry
Acidic condensates with a pH of 3.0 to 5.0 are commonly produced by the burning of natural gasses
within hydronic heating systems. It is very important to maintain a neutral chemistry of the water because
although the aluminum alloys used in the construction of Modulex boilers resist acidic conditions, they are
still vulnerable to highly alkaline environments (pH of 9.0 and above).
Metals, including aluminum, steel, iron, and copper used in hydronic heating systems are highly reactive
to acidic and alkaline chemical environments, so the water must be treated with protectants and buffers to
prevent corrosion of these metals. Because of this, most chemical water treatments have been developed
to protect an array of metals.
13.1.2 Scale and Corrosion
Free oxygen can cause the formation of rust (iron oxides), which degrades metallic materials. Magnetite
is formed in un-inhibited water if there is electrolytic action in the presence of oxygen. Sludge is formed
when calcium compounds, primarily CaCO3, are heated. Rust and magnetite, when combined with
sludge, can form a very hard scale, which significantly reduces system efficiency and life expectancy of
the heating system. Scale reduces heat exchange due to its low heat conductivity and so may cause very
dangerous localized overheating. Waterside corrosion of all heating circuit surfaces is also a major
concern.
13.1.3 Make-up or Feed Water Quality
Make-up or feed water is water added to a closed hydronic system to replenish water lost through
evaporation, maintenance, or leakage. The quality of make-up or feed water, which may contain
dissolved oxygen, minerals and other dissolved contaminants, is extremely important. Such introduced
water must be chemically treated or strictly limited when ensuring neutral chemical conditions in boiler
system water. Generally, any closed hydronic heating system should be restricted from receiving
untreated makeup water of no more than 5% of the total volume of system water per year.
13.1.4 Treating Water to Prevent Freezing
When using anti-freeze solutions, their compatibility with the AERCO Modulex aluminum heat exchanger
and other components of the heating system must be determined prior to use. Traditional HVAC
propylene glycol is not suitable for aluminum heat exchangers: the pH of the glycol at various dilutions is
in excess of 9.5, whereas the pH must be within 6.5 and 8.0 for use with aluminum. There are several
Figure 1: Relief
Valve Point of
Discharge Example
